1. Field of the Invention
The present invention relates to an image processing apparatus and a terminal apparatus suitable for use in video conference or video phone system .
2. Related Background Art
Video phone systems and video conference systems which implement the telephone or conference function over remote sites utilizing images and speech transmitted between these sites via a leased or public digital telecommunication line are known. In such systems, the usable capacity of the telecommunication line is limited, and moving images are thus high efficiency compression coded for transmission. There are two types of bandwith compression for image data: in-frame compression and interframe compression. In in-frame compression, the data is compressed by means of the linear transformation, for example, discrete cosine transformation (DCT) by utilizing the correlation of adjacent pixels in a single frame. In interframe compression, the correlation between the pixels at the same position on the screens of consecutive frames is utilized, and data is compressed by replacing the present pixel data with the pixel data of the past frame on which coding has been already conducted.
A high compression factor can be achieved when both in-frame compression and interframe compression are used. Interframe compression is characterized in that the frame-to-frame correlation weakens in a rapidly moving image, thus rapidly reducing the compression factor thereof. Therefore, in a rapidly moving image, only in-frame compression is used. However, the use of in-frame compression alone is not generally enough to achieve a predetermined compression factor suitable to the capacity of the telecommunication line, and frame thinning is thus performed.
In the video phone system, there have been no such demands for thinning frames so far. However, in the conventional video conference system, it has been proposed to change the direction of a TV camera so that it can follow a participant or speaker as the participant or speaker moves in accordance with the image processing process or speech. It has also been proposed to control the position, direction or zooming of the TV camera from the operation panel on the image transmission side and/or image reception side.
In such cases, the compression factor of the interframe compression operation greatly deteriorates during the movement of the TV camera, resulting in an increase in the amount of codes. As a result, frame thinning is performed for the aforementioned reasons, and an awkwardly moving image is thus displayed on the display screen of the reception side. Also, when the TV camera on the transmission side is operated from the operation panel on the reception side, a time delay that cannot be ignored occurs between the movement of the TV camera and the image displayed on the reception side, making the positioning of the TV camera difficult.